1. Technical Field
This invention relates to the technology of making boxes for forming sand cores, and more particularly to means for venting such boxes without clogging during production use.
2. Discussion of the Prior Art
Core boxes are devices used to form sand cores useful in foundry practices such as casting of metals with internal cavities. The core boxes essentially are tooling with internal cavities contoured to produce the desired core shape. Sand, coated with resin, is blown into the cavities and then cured to produce the finished core. To assure complete filling of the cavity space and optimum hardness and density of the core, vents are required which allow air to escape from the cavities as the sand mix is blown thereinto.
Conventionally, these vents are of either a sheet steel plug construction, the face and sides of which have been cut or perforated, or a hollow steel plug embedded with a mesh screen in the face thereof. These vents are used in extremely large quantities during high-volume core making. During such core production, smaller particles of the resin coated sand are unwantedly blown through the vents, causing the resin to be deposited on its surface. The resin will build up until the vent becomes completely clogged, requiring undesirable cleaning or replacement. Productivity is adversely affected and frequency of cleaning is great.
In any modification of such vents, a designer must be concerned with related factors, such as: (i) the mold releasing properties of the vent structure, (ii) the ease of fabricating the core vent, (iii) the abrasion resistance and heat and chemical resistance of the vent structure, (iv) the opening area or opening rate of the vent to permit the passage of gases while restricting the passage of solid particles, and (v) the structural strength of the core vent to prevent deterioration on handling and reuse.
The prior art sheet metal vent of FIG. 1 is first stamped into a thimble shape 10 having corrugations 11 along the shallow skirt wall 12, and wavy slots 13 cut or crimped into the generally flat face 14 of the vent. The width of the slots is preferably about 0.01-0.02 inch (less than 0.25 mm). Such vent must be expensively nickel plated to provide corrosion resistance and to impart a release capability from a sand mold. The strength of the face material (sheet metal) allows for the slots to be placed close together; moreover, the slots allow for increased opening area or rate (as much as 40% if the slots are closely intertwined). Due to the inherent width of mechanically formed slots, some small particles of resin coated sand will be blown through the vent slots causing resin to be left deposited on the surface of the vent. Resin and sand will eventually build up, completely plugging the vent. This may occur within a frequency of 2-4 hours of use.
The face 14 (head) and skirt 12 (body) of the vent are commercially formed independently and joined by brazing or spot welding. This adds to the expense of the vent fabrication. Earlier versions of the sheet metal vents have used parallel slits 15 which necessitate greater spacing 16 reducing the opening area significantly (compare center section of FIG. 2 with left-hand section of FIG. 2). The parallel slits 15 more readily clog. A more economical vent is that as shown in the right-hand section of FIG. 2; this vent incorporates a mesh screen 17 across the end of a sleeve, the screen providing greater opening area than the parallel slit type, and not only permits some sand/resin to pass through, but is significantly more fragile and is subject to deformation upon cleaning of the mesh.
Therefore, it remains a problem for the foundry industry to find a core vent construction that is less cloggable than current designs and yet acceptably meets such other criteria for a good core vent.